Report 1 (of 5): Changing the Current - Wind Turbines

Introduction

Environmental problems like global climate change and acid rain are known to be caused by chemicals such as carbon dioxide, sulphur dioxide and nitrogen oxide. Such chemicals are by-products of conventional power production which use up fossil fuels. It is known that fossil fuels, such as coal and gas, will at some time in the future run out. As the supply of these fuels continues to be depleted, they become more expensive.

The European Union has made declarations to reduce environmental damage, and to provide and develop the technology to harness sustainable energy resources. Technology for wind turbines has developed a great deal in the last fifteen years and currently, in Europe, wind energy projects provide enough electricity to meet the domestic needs of five million people. The wind energy industry has set itself the target of installing enough wind energy capacity to meet the needs of 50 million people, by the year 2010.

The Rotor and Blades

Most electricity producing turbines have three rotor blades, although some have two, which are usually on a horizontal axis connected to the hub. Rotor diameters can be up to 65 metres, while smaller machines have rotor diameters of around 30 metres. The longer the blades, the larger the area swept by the rotor and hence, the greater the energy output. Blades are made of glass fibre reinforced polyester or wood-epoxy. The shape of the turbine blade is designed so that when air passes over it, the rotor to which it is attached turns.

The Turbine Head or "Nacelle"

The rotor is linked by a shaft directly to the nacelle which contains a gearbox and a generator. As the blades rotate the shaft is turned to drive the generator and produce electricity. Most machines have gearboxes, although the number with direct drive is increasing.

The Yaw Mechanism

The wind direction is detected by sensors which control the yaw mechanism. This turns the turbine so that it always lines up with the wind.

The Tower

Towers are mostly turbular and made of steel. Towers range from 25 to 80 metres high and act as a support to the nacelle and rotor. Electricity produced by the generator comes down the cables in the tower and passes through a transformer into the electricity network.

The Base

Large turbines are built on a concrete base foundation. When a turbine comes to the end of its working life, it is easy to dismantle and its scrap value will cover the cost of dismantling. The base can be dug up or covered, leaving little trace behind.

Preventing Damage in High Winds

Most machines operate at a constant speed of 15-50 revolutions per minute, though new designs have variable speed. Power is controlled automatically as wind speed changes. When wind speed becomes too high, the turbine is shut down to avoid damage.

Stall and Pitch Control

The most common design of wind turbine is the three bladed, stall-controlled, constant-speed machine. Stall and pitch control are a means of controlling power output and describe the design of the blades. On a pitch controlled machine, the angle of the blades can be actively adjusted by a machine control system. This is similar to having brakes on the blades because when they are fully "feathered" they will be stationary in the wind.

Stall control is sometimes known as "passive control" because the blades are aerodynamically designed to perform the same function as a pitch control mechanism, without the moving parts. The twist and varying thickness of the blade mean that when wind speed becomes too high, turbulence occurs behind the blade, shedding some of the wind’s energy and minimising power output at high wind speed. The tips of the blades also have brakes so that they can be brought to a complete standstill if ever necessary.

Energy Output

A unit of electricity = 1 Kilowatt hour

1,000 kilowatts = 1 Megawatt

1,000 megawatts = 1 Gigawatt

1,000 gigawatts = 1 Terawatt

At present the average size of new machines being installed is 600 kilowatts, although machines with the capacity of 1.5 megawatt are available. All wind turbines start operating at a wind speed of 4-5 metres per second and reach maximum power at about 15 metres per second. European wind schemes are typically in clusters of around 10 to 40 turbines, providing enough electricity for between 4,000 and 16,000 households.

Single turbines, often owned in rural areas and by farmers, can produce surplus electricity which the owner can sell back and feed into the local distribution network. This reduces power transmission losses and obviously benefits the owner financially.

Factors in Considering the Installation of a Wind Turbine

The amount and speed of wind on a site is the most important consideration when installing a wind turbine. Wind at twice the speed will increase available energy by eight times. Turbines at a site where the wind speed averages 8 metres per second will produce around 80% more electricity than those where the wind speed is 6 metres per second.

Site access and site ownership will also be a consideration.

The Environmental Impact of Wind Energy

The contribution of wind energy to a national grid of power means that there is less reliance on polluting power plants, such as coal fired power plants. Coal fired plants can emit around 800-1000 grams of carbon dioxide for every unit of electricity they produce. Wind energy saves further emissions from such sources. As electricity supplied by wind energy increases, the need to build further conventional power plants is reduced and such plants can be taken "off-line" when supply exceeds demand.

Compared to conventional power generators and nuclear plants, the environmental impacts of wind turbines are negligible because they do not produce pollutants or have other harmful effects.

A wind farm will obviously change a landscape, although when a community has a good understanding of its benefits and supports the ideas of sustainable energy, they are well received. People may feel more inclined to a wind farm than the building of a nuclear power plant or fuel burning plant, as the health and environmental risks of these are well known. As most parts of a turbine move, it will produce sound at about 45 decibels. This is less than the average noise in a home (50 decibels) or an office (60 decibels). A great deal of effort is put into the design to minimise sound produced by the turbines.

The space taken up by a wind farm need not be damaging to the local environment - sites with the most wind are usually in exposed and rural areas. Although a wind farm might extend over an area of one square kilometre, only 1% of this land is taken up by the base of the turbines. This allows normal agricultural practice to continue because animals can come right up to the base of the machines without danger.

Cost

The most expensive element of installing a wind turbine is in the initial capital cost which is between 75% and 90% of the total cost.

The cost of an actual turbine is between 600 and 900 ECU per kilowatt of power. The cost of project preparation and installation adds another 200 to 250 ECU per kilowatt of power, bringing the total to about 1,000 ECU per kilowatt of power of installed capacity. Ongoing running costs are cheap because wind as a source of fuel is free and turbines have extremely low maintenance costs. They only need servicing once or twice a year and this will usually be to top them up with oil. Consideration does need to be given to the cost of rent for the land and insurance premiums.

The cost for wind energy is coming down and is expected to continue to do so. As the technology for turbines has improved, energy is being produced more efficiently. The increase in the number of wind turbines being manufactured has brought the cost of production down and the trend towards building larger machines reduces the infrastructure costs because fewer turbines are needed for the same output. The cost of financing is also declining as investors gain more confidence in the technology. In comparison, the cost of conventional and nuclear power production is set to increase, meaning wind power will become an even more competitive source of energy supply.

The Future and Benefits of Wind Energy

• In countries where there is limited space for wind farms, such as The Netherlands, there is now the possibility of off-shore wind farms. They have the advantage of generally high wind speeds, although construction and access is more difficult.

• Wind turbines have virtually no environmental impact.

• The cost of wind turbines is set to continue to decline.

• If a country has a significant proportion (between 10 and 20 %) of its energy needs met by wind, it is less reliant on fossil fuel based power, making the country less vulnerable to fuel crisis, as it broadens its energy diversity.

• Over the past two years wind energy capacity has been expanding at an annual rate of more than 30%. Wind turbines with a total generating capacity of over 6,000 megawatts have been built around the world. This figure is expected to more than double by the year 2000.

For further information, please contact:

Intermediate Technology would like to thank the European Wind Energy Association for providing the original materials and pictures of wind turbines.

Further reading available from ITDG Development Bookshop

Where the Wind Blows: An introduction to wind energy
B. Horne
£3.50 1994 pb (Centre For Alternative Technology) ISBN 1898049106

Wind Power for Home and Business: Renewable energy for the 199's and beyond
P. Gipe
£25.00 pb (Chelsea Green) ISBN 0930031644

TVE/ITDG gratefully acknowledge support for the HANDS ON programmes from the UK's Department for International Development (DFID), the European Commission (EC), the UN Foundation and UNDP/The Equator Initiative in collaboration with the Government of Canada, IDRC, IUCN, BrasilConnects and the Nature Conservancy.